1. Technical Field
The present invention relates to a shield structure for electronic circuit parts for shielding electronic circuit parts disposed on a circuit board.
2. Background Art
Electronic circuit parts, such as those used in cellular phones, are disposed or packaged on a circuit board. Specific electronic parts among the mentioned electronic circuit parts, for example electronic parts for handling high frequency wave, are covered with a shield case made of a conductive body, and are shielded electrically and magnetically.
FIG. 6 shows a conventional shield structure for electronic circuit parts. Referring to FIG. 6, a plurality of electronic circuit parts are disposed or packaged on a circuit board 1, and a shield case 2 is installed on the circuit board 1 to cover specific electronic circuit parts. The shield case 2 is of a rectangular solid box shape with an open end, and is fixed by soldering on the circuit board 1 with the open end facing the circuit board, so as to enclose specific circuit parts. This shield case 2 of rectangular solid box shape is placed so that each end face of the four sidewalls contact the circuit board 1, i.e., so that the shield case 2 contacts the circuit board 1 at four end faces thereof, and each end face and the circuit board 1 are soldered with a solder 3. Additionally, reference numeral 3a indicates a faulty soldered part.
FIG. 7 is a shield structure for electronic circuit parts disclosed in the Japanese Laid-open Patent Application No. 27691/1997. The open-end faces of the shield case 2 are provided with four fixing hooks 4 projecting in L-shape. The circuit board 1 is provided with rectangular holes 5 corresponding to the four fixing hooks 4, and metallic pads 6 each adjacent to each of the rectangular holes 5. Each of the four fixing hooks 4 of the shield case 2 is inserted through each rectangular hole 5, and folded so as to be in contact with the metallic pad 6, and then fixed to the circuit board 1 by soldering. In this structure, the shield case 2 is installed on the circuit board 1 sustained at four points.
As described above, the shield cases has been conventionally installed on the circuit board either by soldering the four faces as shown in FIG. 6, or by soldering the four sustaining points as shown in FIG. 7. However, the sidewalls of a shield case of rectangular solid box shape may be warped or distorted because the shield cases are generally molded by bending or pressing process. If any of the sidewalls of the shield case is warped or distorted in case of the four-face contact as shown in FIG. 6 and the contact faces do not constitute a plane surface, the four faces will not fully contact the circuit board, and consequently sufficient attaching strength cannot be secured by soldering, which may eventually result in an accident that the shield case gets out of and falls from the circuit board.
Moreover, in the four-point sustention structure as shown in FIG. 7, if the shield case is warped or distorted, it may be impossible to insert the four fixing hooks 4 through the corresponding four rectangular holes 5, or to fold any of the fixing hooks 4 though the insertion is barely achieved. Consequently, the shield case cannot be installed on the circuit board.
It is certain that such disadvantage caused by warp or distortion of a shield case can be solved by reworking each contact face of the shield case to improve the flatness precision of the four contact faces in case of four-face contact as in FIG. 6, or by eliminating the warp or distortion through a heat treatment of the shield case in case of four-point sustention structure as in FIG. 7. But, the aforementioned reworking or heat treatment requires extra operations, which will result in a disadvantage of cost increase.
In view of the foregoing disadvantages incidental to the prior arts, and object of the present invention is to propose an improved shield structure for electronic circuit parts, which allows an easy installation of a shield case on a circuit board with more strength and firmness, even if the shield case is warped or distorted.
To accomplish the foregoing object, a shield structure for electronic circuit parts according to the present invention comprises a circuit board on which a plurality of electronic circuit parts are disposed and a shield case which is installed on said circuit board to enclose and shield specific electronic circuit parts among said plurality of electronic circuit parts; wherein said shield case comprises a frame member including four sidewalls and a cover member covering the farther end of the frame member from said circuit board; said frame member includes a supporting member for sustaining said frame member on said circuit board and an end face confronting the mentioned circuit board; and said supporting member is composed of three projections protruding from the said end face toward the mentioned circuit board.
As a result of such an arrangement, the shield case can be securely joined to the circuit board by three-point sustention, and fixed securely and firmly at the joints, without any additional subsequent treatment such as reworking or heat treatment.
It is preferable that, in the shield structure for electronic circuit parts according to the invention, said circuit board is provided with a circuit pattern formed thereon and a solder bed formed on said circuit pattern, and each of said projections is soldered to said circuit pattern penetrating through the solder bed, and gap is formed at least one part between said end face and the circuit pattern, and said gap is not larger than 0.1 millimeter.
As a result, the above described shield structure can secure a sufficient shielding effect, while absorbing the warp or distortion of a shield case as a variation in the gap.
It is also preferable that, in the shield structure for electronic circuit parts according to the present invention, said circuit board is provided with a circuit pattern formed thereon and a solder bed formed on said circuit pattern, and each said projections is soldered to said circuit pattern penetrating through the solder bed, and gap is formed at least one part between said end face and the circuit pattern, and a solder is inserted in at least one part of said gap.
As a result, the above described shield structure can secure a more firm shielding effect, while absorbing the warp or distortion of a shield case as a variation in the gap dimension.
It is also preferable that, in the shield structure for electronic circuit parts according to the invention, the first sidewall of said four sidewalls is provided with the first and the second projections of said three projections, and the second sidewall of said four sidewalls confronting said first sidewall is provided with the third projection of said three projections.
As a result, the three-point sustention structure can be stabilized all the more.
It is also preferable that, in the shield structure for electronic circuit parts according to the invention, said first, second and third projections are placed so as to fall on each vertex of an isosceles triangle.
As a result, the three-point sustention structure can be stabilized all the more.
It is also preferable that, in the shield structure for electronic circuit parts according to the invention, said first sidewall is provided with an extension extending across the mentioned circuit board in the direction of thickness thereof, and said first and second projections are placed on both sides of said extension.
As a result, the positioning and close joint of the first sidewall and the circuit board can be achieved by means of the mentioned extension.
It is also preferable that, in the shield structure for electronic circuit parts according to the invention, said second sidewall is provided with two extensions extending across said circuit board in the direction of thickness thereof, and said third projection is placed between each of these extensions.
As a result, the positioning and close joint of the second sidewall and the circuit board can be achieved by means of the mentioned extensions.
Further, a shield structure for electronic circuit parts according to the invention comprises a circuit board on which a plurality of electronic circuit parts are disposed, and a shield case which is installed on said circuit board to enclose and shield specific electronic circuit parts among said plurality of electronic circuit parts; wherein said shield case is provided with a frame member including first and second sidewalls confronting each other, third and fourth sidewalls confronting each other and a cover member covering the farther end of the frame member from said circuit board; said first sidewall is provided with an extension extending across said circuit board in the direction of thickness thereof and two projections placed on both sides of the extension; said second sidewall is provided with two extensions extending across said circuit board in the direction of thickness thereof and a projection placed between said two extensions; and said third and fourth sidewalls are provided with end faces confronting said circuit board, each of said projections protruding to said circuit board for supporting said shield case.
As a result of such arrangement, the positioning and close joint of the first and the second sidewalls and the circuit board can be achieved by means of the mentioned extensions.